1. Field of the Invention
The present invention relates to an apparatus for calculating the correlation between two sets of data, and more particularly to such an apparatus for calculation of correlation, for example, after photoelectric conversion in optical range finding with two photoelectric converting element arrays.
2. Description of the Prior Art
U.S. Pat. No. 4,078,171 discloses an apparatus for detecting the state of focusing from the correlation between two sets of photoelectric output signals obtained from a spatial image. Also U.S. Pat. No. 4,185,191 discloses a focus detecting apparatus adapted for use in a camera of the through-the-lens system.
In such prior art, two sets of data a, b corresponding to photoelectric output signals are obtained from an array of small lenses provided in the vicinity of a focal plane of an objective lens and from a set of photoelectric converting elements provided in pairs in the vicinity of the focal point of each small lens, and the data set a is shifted in succession with respect to the data set b for determining the correlation value between said two data sets at each shifted position, whereby an amount of shift giving the strongest correlation is determined among plural correlation values. In this manner, it is possible to detect the state in which the data sets a, b provide the largest correlation.
However, such apparatus is not suitable for a case requiring high-speed calculation for a set including a large number of data, since an enlarged range of shift for investigating the correlation requires time-consuming repetitive calculations. Particularly in a photographic camera, a long calculating time leads to an insufficient response speed in photographing a fast moving object or in photographing with a motor-driven camera.
Also the conventional apparatus described above are incapable of sufficiently precise measurement due to the lack of information if the number of data compared in calculating the correlation is limited, for example equal to or less than 20. Also, even if the number of data to be compared is large, it is still not possible to detect the image displacement with such a precision as is obtained in a case where the width of each photoelectric converting element is divided into several, again because of the shortage of information, since the data processing is conducted after the photoelectric converted output signals are simply binary encoded.